OGC is incrementally changing how schemas will be hosted. A new revision
of the Specification Best Practice policy document (06-135r5) is in the
works which should clarify the practices.

OGC is moving to host the schemas using a 2 digit version number so that
dependent documents (schemas) will not have to change each time a
schema is corrected (by a corrigendum). The schemas actual version
number will be kept in the version attribute on the schema element which
will be used to signify that there has been a change to the schema. Each
previous revision will be available online in a ZIP archive.

The LATEST version is the M.N directory where 
 * M is the major version
 * N is the minor version
The latest bugfix version now is always in the M.N directory and 
documented in the version attribute on the schema element. The older
versions are now archived in the -M_N_X.zip files.

Previously the OGC used M.N.X where
 * M is the major version
 * N is the minor version
 * X is the bugfix (corrigendum) version
These will be left here for historical reasons.

 -- 2009-03-10